1. Field of the Invention
The invention relates to ear wax barriers for custom in the ear hearing instruments in accordance with the general definition of patent claim 1.
2. Technical Background
Cerumen traps which prevent the ingress of ear wax into the hearing instrument and other cerumen traps which reduce the likelihood of ear wax blocking the sound outlet are already known.
From U.S. Pat. No. 4,972,488 which describes clearly detailed barrier designs which use a fine mesh screen in the sound channel wherein if sufficiently small screen holes are used, will eventually clog with wax and conversely when mesh is made with wider screen holes, wax will eventually migrate across the screen and damage the transducer. Such cellular synthetic screens can increase acoustic impedance between the transducer and the ear drum which may modify the frequency response and acoustic gain of the hearing aid device.
From U.S. Pat. No. 5,105,904 arrangements which utilize wax filters or caps necessitate the need to replace such filters when clogged with wax. Clogging can occur gradually depending upon variances of cerumen production in different hearing instrument wearers or immediately upon inserting the hearing instrument into the ear canal.
In the gradual clogging process, the wearer's perceived sound quality may gradually worsen evidenced by acoustic feedback or lack of output. The wearer must purchase or otherwise obtain additional filters and tools for replacement of the filters. First the wearer needs to visually verify the filter or screen needs changing or the cap is clogged. Visual acuity and finger dexterity are necessary for proper replacement and realignment of such filters or caps. Other mechanical, internal defects can develop in nearing instruments which display the same failure characteristics as wax clogging does, thereby leading to frustration when filter replacement does not alleviate an internal failure. Often times, it is more desirable for a trained hearing aid professional to clean the hearing instrument and verify specifications in order to reduce the wearer's frustration and chance of improper installation resulting in filters, screens or caps falling off the unit or into the wearer's ear canal. Thus it is desirable to have a barrier which does not need replacement over the life of the hearing aid.
If the filter, screen, or cap clogs when inserting the hearing aid, the filter acts as a wax "scoop", particularly if the wearer's canal diameter is small in respect to the diameter of the filter. Thus it is desirable to keep such barriers as small as possible to reduce the incidence of insertion clogging.
Three piece barrier systems are known which consist of a metallic hinge pin, inserted into a sound outlet base--typically made of Acrylonitrile-Butadiene-Styrene resin, "Cycolac", Tenite, Poly amide, or similar injection molded thermoplastic--and a barrier door, also made of a similar plastic, which attaches to the hinge pin.
The sound outlet base incorporates a bore to allow the outlet of sound from the transducer, and a small detent cavity which accepts a latch mechanism from the barrier door, and two small cavities parallel to the base which accept the hinge pin.
The sound outlet base perimeter is square. The side opposite the hinge pin is flat. This flat side is affixed to the tip of the hearing instrument shell (perpendicular to the long axis of the ear canal), typically with Methyl Methacrylate, Cyanoacrylate "super glue", or similar bonding agent of the aforesaid plastics. The square base must be trimmed and then buffed to match the contour of the tip of the wearer's hearing aid. The buffing process can disrupt the placement of components within the shell often resulting in non-conforming specifications such as acoustic feedback, or shorting. The buffing process can also reduce the size of the canal tip resulting in an improper fit for the hearing aid wearer. Thus a barrier is desirable which could eliminate this trimming process.
This three component barrier system utilizes the barrier door to prevent clogging of the sound outlet during insertion. The barrier door has a hinge at one end to rotate about the hinge pin and a latch at the other end to keep the door closed. Thus it is the barrier door hinge in combination with the hinge pin which attaches the barrier door to the sound outlet base and it is the latch on the barrier door which keeps the barrier door closed and parallel to the sound outlet base.
The barrier door when snapped onto the hinge pin and closed, leaves a clearance so that sound is not appreciably impeded once it exits the sound outlet bore. Such a clearance is desirable for a wax barrier which is large enough not to reduce the transducer output or significantly change the acoustic impedance of the hearing instrument.
Effective in the way it prevents wax from being scooped into the sound outlet, and in the elimination of replacement filters, it requires periodic cleaning when ear wax collects near the clearance between the base and door. The cleaning process is usually accomplished by unlatching and opening the barrier door, and then brushing away wax with a small brush. Difficulties arise when the plastic door hinge fatigues during the life of the hearing instrument, due to periodic cleaning (typically daily), and thus lose grip on the hinge pin. The wearer then risks the possibility of losing the small door or even an unhinged door falling into the ear canal while wearing the hearing instrument. Thus it is desirable for a barrier unit which minimizes fatigue on any such hinge or latch which connects the barrier to the hearing instrument.
Such barriers which, when open, extend the effective length of the hearing instrument (along the long axis of the ear canal), can possibly injure a wearer's ear drum if the end of the hearing instrument is already close in proximity to the ear drum. Thus it is desirable for a barrier which poses no threat of injury to the wearer's ear drum, particularly if the barrier is inserted into the ear canal when open.